Hey, glad to see you joining the game jam community!
I really like the minimalistic visuals as it does make it very easy to tell what is what and it is very easy to play yet it still poses a challenge! I really like that! I am also a big fan of the game modifications that change it up a bit.
As far as improvements go, I wouldn't stress too much about it as it is your first game jam and you've only been using unity for half a year so really I'd say that this is a more great start! But I do want to mention that I feel the camera is a little to close to the player and the menu, while looks great colour-wise, is hard to select the correct button and I think you should make the non-button text be smaller.
I think that (if you are using unity) you could use the 'scale with screen size' canvas option so that the menu can be more spaced out and the in match UI doesn't get in the way when you go into full screen.
But like I said earlier, don't worry about it too much as this is a great start! Just focus on what you achieved for now!